This invention relates to an overload indicator or mechanical fuse that can be used to determine if a force level has exceeded an acceptable predetermined amount of force. More particularly, this invention relates to an overload indicator or mechanical fuse with an overload retainer that maintains a connection between a force generator and a load after an overload event occurs.
An overload indicator or mechanical fuse typically includes a low cost component that can be sacrificed to prevent damage to more costly components. By way of example, a shear pin can be used to connect a propeller to a drive shaft on an outboard motor. If the propeller strikes an obstruction, the shear pin can break to prevent damage to the motor""s drive train. Shear pins are usually mounted with their longitudinal axis oriented in a direction transverse to the applied load. Devices that use shear pins are disclosed in at least three United States Patents, including U.S. Pat. No. 5,122,007 to Smith, U.S. Pat. No. 4,330,926 to McCall, and U.S. Pat. No. 5,466,082 to Shearer.
Overload indicators or mechanical fuses can also use sacrificial components which have a longitudinal axis oriented in the direction of the applied force. For example, a mechanical fuse can be interposed between a helicopter and a load carried by a cable depending from the helicopter. If the load strikes an object, the mechanical fuse can break, thereby releasing the load to avoid damage to, or even the destruction of, the helicopter. Examples of longitudinally mounted mechanical fuses are disclosed in at least two United States patents, including U.S. Pat. No. 5,599,129 to Clifton and U.S. Pat. No. 6,007,267 to VanHom. Additional mechanical fuse type devices are disclosed in U.S. Pat. No. 3,675,282 to Summers et al, U.S. Pat. No. 4,846,769 to Allen, U.S. Pat. No. 5,895,892 to Braun, U.S. Pat. No. 4,755,632 to Pelet et al, and U.S. Pat. No. 3,185,415 to Walker.
In some applications, an operator may not be aware that an overload situation has occurred until the mechanical fuse fractures, severing the connection between the force generator and the load. This approach may prevent damage to the force generating mechanism at the possible expense of destroying the load, or vice versa. Depending upon the cost of the item that is damaged or destroyed, this may not be a desirable result. This result can also be undesirable if the item that is suddenly unconstrained, subsequent to the fracture of the mechanical fuse, is free to impact adjacent structures or personnel or fall into areas where retrieval will be difficult or impossible.
According to one aspect of the invention, an overload indicator apparatus is provided for use in connection with a force generator. The force generator is used to apply a force to a load via the overload indicator, and the overload indicator maintains a connection between the force generator and the load while indicating whether force applied to the load is greater than a predetermined acceptable amount of force.
The overload indicator includes a first support or plate member, a second support or plate member spaced away from the first plate member, and a tensile member. The first support member can be connected to the force generator, and the second support member can be connected to the load. The tensile member can be positioned between, and in load bearing communication with, the first support member and the second support member, and is adapted to support at least part of the force when the force is less than substantially the predetermined amount.
The overload indicator further includes an overload retainer comprising at least one beam, the beam having a first end connected to the first support member and a second end connected to the second support member. The beam is adapted to support at least part of the force when the force is greater than substantially the predetermined amount of force.
An indicator means indicates that the force applied to the load is greater than substantially a predetermined acceptable amount of force. A variety of indicator means may be used. For example, the indicator means may be visual, and can comprise the tensile member, the first support member, the second support member, an electronic switch connected to a visual output device, or a combination of these members. The indicator means may also be audible, comprising the tensile member, an electronic switch connected to an audible output device, or a combination of these elements.
An example of an indicating means that can be both visual and audible is the tensile member. The tensile member can be selected to break when the force is greater than substantially the predetermined amount of force. The tensile member can break with an audible xe2x80x9cpopxe2x80x9d to alert the user that an overload situation has occurred. Moreover, even if the xe2x80x9cpopxe2x80x9d is not audible, a visual examination of the tensile member can still reveal the break. The tensile member can include a weakened portion, such as the middle portion between the first and second support members, that is adapted to break at a specific position. The tensile member can be removably connected to one or both of the first and second support members, which permits relatively easy replacement of broken tensile members and also the selection and use of various tensile members corresponding to the desired predetermined acceptable amounts of force.
For example, a first fastener can releasably secure the first tensile end to the first support member, the first fastener being removable from a first exposed side of the first support member. Likewise, a second fastener can releasably secure the second tensile end to the second support member, the second fastener being removable from a second exposed side of the second support member. In such an arrangement, when the first fastener and the second fastener are removed, the tensile member can be removed from the first support member and the second support member without having to first disassemble the support members and overload retainer.
Either the first or second support members, or both, can be moveably connected to the ends of the beam in the overload retainer. The far ends of the beam can each have a stop member. When the force is less than substantially the predetermined amount of force, a support plate member that is moveably connected to the beam will be in an underload position, and when the force is greater than substantially the predetermined amount of force, such support member will move to an overload position. In the overload position, such support member is closer to the stop member than when in the underload position. A force absorber may be positioned between the support member and the stop member to limit impact loads that would otherwise occur between such support plate member and a stop member. The support members compress the force absorbers when moving into the overload position, and the stop members retain the force absorbers and support members on the beam.
Either or both of the support members can comprise a visual overload indicating means, since the user of the apparatus can determine if an overload situation has occurred by visually ascertaining whether the support members are in an underload or overload position. The support members can also comprise an audible indicating means.